Aging is accompanied by changes in the level of neurometabolites. However, their role in vital behavioral functions is still unclear. We aimed to explore the impact of aging on the neurochemical mechanisms underlying action selection. Young (YA) (n = 25) and older adults (OA) (n = 26) performed a simple (SRT) and a choice (CRT) reaction time tasks. Magnetic resonance spectroscopy was utilized to track task-induced modulations in GABA and glutamate in the sensorimotor cortex (SM1) and dorsolateral prefrontal cortex (dlPFC). Results showed that (i) SM1 Glx levels were higher during the SRT in the full sample, (ii) Glx modulation in the dlPFC predicted better behavioral performance in the SRT only in YA, and iii) a task-induced increase in GABA and Glx in the dlPFC was related to action selection learning in the full sample. Our findings highlight an important role of neurometabolic modulation during action selection and learning.